Two gardens with the same surface area can hold different amounts of plant available water. Soil properties and effective root depth both matter. A surface area measurement on its own cannot tell you when a watering interval has used up the chosen reserve.
The Soil Water Storage Calculator uses volumetric field capacity and wilting point to calculate available water across the entered root depth. It then applies an allowed depletion percentage and converts that refill depth into gross irrigation litres.
Thirty centimetres of root depth
For field capacity of 30% by volume and wilting point of 15%, the difference is 15 percentage points. Across a 30 cm root zone, total available water is 45 mm.
At 40% allowed depletion, the net refill depth at that trigger is 18 mm. For 20 m² of garden, this is 360 net litres. With 90% application efficiency, the gross refill becomes 400 litres.
That result describes refill at the specified depletion threshold. It is not a measurement of the moisture currently present, and it does not say that every watering session should deliver 400 litres.
Percentages must describe the same soil basis
Both field capacity and wilting point are volumetric percentages in this tool. A laboratory or reference value stated on a mass basis should not be copied directly into these fields. The calculation cannot convert between those bases without additional soil information.
Wilting point must be below field capacity. If the entries are reversed or equal, the calculator rejects them instead of reporting a usable water reserve that makes no physical sense under this model.
Use suitable soil measurements and a root depth relevant to the crop and site. The default values are examples, not measurements for clay, sand or any Pakistani city. A shallow effective root zone changes storage even if the bed or soil profile extends much deeper.
This is not a complete watering schedule
Allowed depletion is an entered planning choice. The tool does not select a crop stress threshold or monitor the soil to detect when it has been reached. It also does not account for layered soil, groundwater, salinity or day by day rainfall.
If you have a period water demand estimate, Crop Water Budget Calculator can help keep crop use and effective rain separate. To turn a selected refill volume into minutes, use Drip Irrigation Runtime Calculator with the actual operating zone.
Transfer the net refill quantity carefully. The 400 litre example already includes application loss, so applying the same 90% efficiency again would inflate the order. Save the measured soil basis and chosen trigger alongside the litres so later changes do not lose that context.